1. Technical Field of the Invention
The present invention relates generally to flow control devices, and more particularly to a valve including an axial style trim which is adapted to facilitate a pressure drop along the axis of the trim and is well suited for use in conjunction with erosive fluids.
2. Description of the Related Art
As is known in the fluid flow control field, the control of erosive and cavitational forces is a primary objective of the design of many high pressure valves. There is currently known in the prior art valves which include shafts and plugs that are linearly displaced during normal operation of the valve. Within these valves, which are often referred to as linear displacement valves, the valve plug of the valve is disposed and moveable within a flow control element such as a disk stack or valve cage which defines a multiplicity of tortuous and non-tortuous fluid passages. Certain linear displacement valves are configured for “over plug flow” wherein fluid flows radially inward into the interior of the flow control element from the exterior thereof, with the fluid undergoing energy loss as a result of the flow radially inwardly through the flow control element. In this arrangement, the valve is opened by lifting the valve plug off a complimentary seat which thus allows the fluid to flow from the interior of the flow control element out of the valve via the unblocked valve seat. Conversely, the movement of the seating surface of the valve plug into sealed engagement with the complimentary seating surface of the valve seat facilitates a closed or shut-off condition for the valve.
Other linear displacement valves are configured for “under plug flow” wherein fluid flows radially outward from the interior of the flow control element to the exterior thereof, with the fluid also undergoing energy loss as a result of the flow radially outwardly through the flow control element. In this arrangement, the valve is opened by lifting the valve plug off a valve seat which thus allows fluid to flow into the interior of the flow control element via the unblocked valve seat. Conversely, the movement of the seating surface of the valve plug into sealed engagement with the complimentary seating surface of the valve seat facilitates a closed or shut-off condition for the valve.
Over plug flow and under plug flow linear displacement valves are sometimes employed in applications wherein an erosive fluid (e.g., water with abrasive sand) is channeled therethrough. The channeling of erosive fluids through linear displacement valves including flow control elements which comprise stacked disk designs or valve cage/cartridge designs gives rise to certain potential problems. More particularly, the potential problems lie in the susceptibility of the fluid passages defined by such disk stacks or valve cages becoming plugged by dirt or other debris in the fluid stream. In this regard, the blocking of the fluid passages of the flow control element with debris often causes a loss of both flow and control within the valve.
In recognition of these deficiencies, there has also been developed in the prior art high-pressure liquid letdown valves which are uniquely designed to operate reliably in harsh environments involving the flow of dirty liquids. These valves, often referred to as “dirty service” valves, typically include an axial trim which is adapted to facilitate a pressure drop along the axis of the trim, versus radial designs such as the disk stack and valve cage type trims discussed above. Since the axial trims are conducive to larger flow passages, they are better suited for use in conjunction with erosive fluids. One currently known variety of axial trim is a notch style trim such as that found in the 78400/18400 Series Masoneilan® LincolnLog® control valves provided by Dresser, Inc., and the Fisher® Notch Flow® control valves of Emerson Electric, Inc. Though these existing notch style axial trim valves are well suited for use with erosive fluids and provide high flow resistance, they possess certain deficiencies which detract from their overall utility.
One such deficiency relates to a lack of flow control. These control problems are attributable to the fact that currently known notch style axial trims possess a linear flow characteristic (i.e., Cv vs. axial trim stroke length). Another deficiency lies in the reduced Cv capacity of currently known notch style axial trims, such reduced capacity being attributable to their design coupled with the relatively short stroke length thereof within the valve. Additionally, axial trims, including the notch style axial trims discussed above, have not successfully been integrated into axial style bodies, and thus are not well suited for use in conjunction with rotary actuators.
The present invention effectively overcomes many of the deficiencies of prior art axial trims, including notch style axial trims, by providing a dirty service valve including an axial trim which has an extended stroke linear flow characteristic and, as a result, increased Cv capacity relative to valve plug size. Further, the axial trim integrated into the valve of the present invention may be configured to have a non-linear flow characteristic which, coupled with the extended stroke length thereof, provides improved flow control in addition to increased Cv capacity. The valve of the present invention may also include an axial body or housing which accommodates the axial trim, and possesses the advantages of being much lighter in comparison to bodies used in radial trim valves, with the axial body also making the use of rotary actuators more feasible. The use of rotary actuation reduces costs, and also provides advantages in relation to fugitive emissions. These, as well as other features and advantages of the present invention, will be discussed in more detail below.